Paris Métro Line 15 is one of four new lines of Grand Paris Express, a major expansion project of the Paris Métro. Currently under construction, the line will provide a new orbital route through the suburbs of Paris, servicing the departments of Hauts-de-Seine, Val-de-Marne and Seine-Saint-Denis. The southern section of the line is planned to open in 2025, with the completed line planned to open in the early 2030s. Line 15 will be fully automated, along with all other Grand Paris Express lines, and when completed, it will be the longest underground rapid tunnel for passenger traffic in the world.

The Paris Métro, operated by the Régie autonome des transports parisiens (RATP), is a rapid transit system in the Paris metropolitan area, France. A symbol of the city, it is known for its density within the capital's territorial limits, uniform architecture and unique historical entrances influenced by Art Nouveau. The system is 226.9 kilometres (141.0 mi) long, mostly underground. It has 308 stations of which 64 have transfers between lines. There are 16 lines, numbered 1 to 14, with two lines, Line 3bis and Line 7bis, named because they used to be part of Line 3 and Line 7, respectively. Line 1, Line 4 and Line 14 are automated. Lines are identified on maps by number and colour, with the direction of travel indicated by the terminus.